M. W. P. TWEEDIE On the Crabs of the Family Grapsidae in the Collection of the Raffles Museum By M. W. F. TWEEDIE, M.A. Plates XIV, XV . Of the material described in the following pages by far the greater part has been collected during the last three years, mainly in mangrove swamps around Singapore Island and at a few other Malayan localities. An account is given of all the forms that are identifiable with certainty, or of which there is material adequate for description, but there remain a few species belong- ing to the genera Pachygrapsus, Ptychognathus and Sesarma which are represented by single specimens or by juvenile series, for the proper treatment of which further collecting and study is necessary. In a number of cases published descriptions have been found inadequate for determination with certainty, and recourse has been had to comparison with types or well authenticated speci- mens. This would have been impossible without the generous assistance of zoologists in various parts of the world. Acknowledgements in this respect are due to Dr. Mary J. Rathbun, Dr. Isabella Gordon, Prof. Dr. H. Balss, Prof. Dr. H. Boschma, Dr. B. N. Chopra and Dr. K. Stephensen. Some of the material from Christmas Island was previously studied by Mr. Melbourne Ward, and two species of terrestrial Sesarmse were identified by Dr. J. Roux. When measurements are given the posterior breadth of the carapace is taken between the bases of the last pair of legs. The figure for the total length of the abdomen is obtained by measuring the joints separately, as if it is measured as a whole its curvature gives rise to an error resulting in an underestimate of its true length. Systematic.— • Pachygrapsus quadratus sp. n. Sesarma (Sesarma) gemmifera sp. n. Sesarma (Sesarma) singaporensis sp. n. Sesarma (Parasesarma) calypso lanchesteri subsp. nov. Sesarma (Parasesarma) rutilimana sp. n. Sesarma (Chiromantes) siamensis Rathbun=Sesarma fasciata Lanch. [ 44 ] BULL. RAFFLES CRABS OP THE FAMILY GRAPSIDJE Sesarma (;Sesarma) smithii H. Milne-Edwards referred to the subgenus Sarmatium. The types of the new forms will be deposited in the British Museum. Sub-family GRAPSIN^E Genus Grapsus Lamarck Grapsus strigosus (Herbst). 1799. Cancer strigosus Herbst, Krabben, iii, 1, p. 55. 1918. Grapsus strigosus, Tesch, "Siboga"-Exped., xxxixc, p. 71. Material.—Two males and three females from the Horsburgh Lighthouse, off the south-east point of Johore, April, 1934. Grapsus intermedins de Man. 1888. Grapsus intermedins de Man, Arch. Naturgesch., Jahrg. liii, p. 865. 1918. Grapsus intermedins, Tesch, "Siboga"-Exped., xxxixc, p. 71. 1984. Grapsus intermedins, Ward, Bull. Raffles Mus. ix, p. 24. Material.—A male and two females from Christmas Island, Indian Ocean, 1932. These specimens were identified and commented ori by Melbourne Ward, (l.c.). Genus Geograpsus Stimpson Geograpsus grayi (H. Milne-Edwards). 1853. Grapsus grayi Milne-Edwards, Ann. SeL Nat. Zool. (8) xx, p. 170. 1918. Geograpsus grayi, Tesch, "Siboga"-Exped., xxxixc, p. 74. Material.—One male from Christmas Island, Indian Ocean, 1932. Geograpsus crinipes (Dana). 1851. Grapsus crinipes Dana, Proc. Ac. Nat. Sci. Philad., 1851, p. 249. 1918, Geograpsus crinipes, Tesch, "Siboga"-Exped., xxxixc, p. 74. Material.—Two females from Christmas Island, Indian Ocean, 1932. Both this and the last species were recorded by Caiman1 from Christmas Island. i> Caiman, Proc. Zool. Soc. 1909, p. 705. Genus Pachygrapsus Randall. Pachygrapsus planifrons de Man. 1888. Pachygrapsus planifrons de Man, Arch. Natnrgesch, Jahrg. liii, p. 868 (Noordwachter Island, Bay of Batavia). 1918. Pachygrapsus planifrons, Tesch, "Siboga"-Exped., xxxixc, p. 77. 1934. Pachygrapsus planifrons, Ward, Bull. Baffles Mus., ix, p. 25. Mus. 12, 1980. [46] M. W. F. TWEEDIE Material.—A series from Christmas Island, Indian Ocean. These specimens were identified and commented on by Melbourne Ward (l.c.). Pachygrapsus natalensis Ward. 1934. Paehygrap8U8 natalensis Ward, Bull. Raffles Mus., ix, p. 25 (Christmas Island, Indian Ocean). Material.—One female paratype from Christmas Island. Pachygrapsus minutus A. Milne-Edwards. 1873. Pachygrapsus minutus A. Milne-Edwards, Nouv. Arch. Mus. Paris, ix, p, 292 (New Caledonia). 1909. Seaarma murrayi Caiman, Proc. Zool. Soc. London, p. 708. 1934. Pachygrapsus minutus, Balss, Zool. Anz., cvi, 10, p. 229. 1934. Pachygrapsus murrayi, Ward, Bull. Raffles Mus., ix, p. 25. Material.—A series of specimens from Christmas Island, Indian Ocean, identified by Melbourne Ward (l.c.). I follow Balss (l.c.) in reducing P. murrayi to the synonymy of P. minutus. Pachygrapsus quadratus sp. n. Plate, XTV, fig. 1. 1900. ? Pachygrapsus transversus, Lanchester, Proc. Zool. Soc. London, 1900, p. 755, under Metopograpsus oceanicus J. & L. Type.—An adult male collected at Siglap, Singapore in Sept. 1933 by a native collector of the Raffles Museum. Material.—Two adult males from Siglap, Singapore including the type, an adult female from Penang <1935) and seven small specimens of both sexes from Pulau Pisang, an island in the south part of the Malacca Strait (1934). Characters.—A species closely allied to P. transversus (Gibbes), but distinguished by the flatter and more quadrate carapace, which is far less convergent backwards, the ratio of the posterior to the anterior breadth being 1: 2.4 (in the type of quadratus) against 1:3.05 (in a male transversus from Brazil) ;l by the absence of well marked transverse ridges on the carapace, and of the conspicuous brown patches on the fingers of transversus. Description.—The ornamentation of the carapace consists of the following elements: A transverse ridge extends a little way on to the carapace from just in front of the epibranchial tooth and a shorter transverse line lies just behind it. From the Through the kindess of Dr. M. J. Rathbun and of the Direction of the U. S. National Musenm I have been able to compare specimens of P. transversus from the coast of Brazil with the present species. [ 46 ] BULL. RAFFLES CRABS OF THE FAMILY GRAPSID^S epibranchial tooth a ridge runs obliquely backwards, and behind and parallel to it are 8 or 9 oblique lines on the branchial regions. On the gastric region are numerous short, faint, transverse, beaded lines. Of the post-frontal lobes the outer pair are very slightly the broader. The anterior margins of all four lobes lie nearly in one straight line, those of the outer being only slightly in advance of and oblique to the inner. The front is rather prominent and its margin nearly straight in the middle part, having only a very slight median emargination. At each side it slopes back to the interior orbital angle, and is beaded in all its extent. The chelae are subequal or unequal, the right, in most cases, being larger than the left. In adults the lower border of the immovable finger is markedly convex. The female exhibits no secondary sexual characteristics except that the chelae are rather smaller and the carapace broader, particularly posteriorly, so that it has even more the appearance of being almost quadrate. Remarks.—Lanchester (I.e.) recorded specimens of Pachygrapsus from Malacca which he identified as P. transversus, but pointed out that, apart from the condition of the internal subocular lobe, they resemble Metopograpsus oceanicus so closely that they might be regarded as a variety of it. P. quadratus does bear a strong resemblance to M. oceanicus in respect of the ornamentation of its carapace and the development of its legs and chelipeds. As Tesch1 points out, P. transversus could not possibly be confused with M. oceanicus, and it seems probable that Lanchester's specimens were P. quadratus, which is, however, readily distinguishable from AT. oceanicus by the more quadrate carapace and the narrower front, as well as by the reduced internal suborbital lobe. Measurements of the type. Carapace. Anterior breadth .. .. 22.6 mm. Breadth between epibranchial teeth 23.9 Median length 20.4 Posterior breadth 9.5 Breadth of front 13.3 Right Chela. Length 19 Height of palm 10.5 Length of dactylus .. 11 Mus. 12, 1936. [ 47 ] M. W. F. TWEEDIE Penultimate walking leg. Length of merus 15 mm. Breadth of merus 7 Combined length of carpus and propodus 17 Length of dactylus .. 5 Abdomen. Length 14 Breadth at third segment 11 Length of penultimate segment 3 Breadth at base 6 Length of last segment 3 Breadth at base 4 i- Tesch, "Siboga"-Exped., xxxixc, (1918), p. 82. Genus Metopograpsus H. Milne-Edwards. Metopograpsus messor gracilipes de Man. 1891. Metopograpsus messor var gracilipes de Man, Notes Leiden Mus., xiii, p. 49 (Pacific). 1895. Metopograpsus messor var gracilipes, de Man, Zool. Jahrb. Syst., ix, p. 75. 1918. Metopograpsus messor subsp. gracilipes, Tesch, "Siboga"- Exped., xxxixc, p. 79. Material.—Three males and two females from Singapore and neighbouring islands and two males from Pulau Pisang in the south part of the Malacca Strait. Metopographsus oceanicus (Jacq. & Lucas). 1842. Grapsus oceanicus Jacquinot et Lucas Voy. "Astrolabe" et Z616e, Crust., p. 73. 1918. Metopograpsus oceanicus, Tesch, "Siboga"-Exped, xxxixc, p. 81. Material.—Numerous specimens from Singapore and neighbouring islands. Metopograpsus latifrons (White). Plate XIV, fig. 2. 1847. Grapsus latifrons White, Voy. "Fly", ii, p. 337. 1853. Metopograpsus maculatus H. Milne-Edwards, Ann. Sci. Nat. Zool. (3) xx, p. 165. Material.—Seven males and seven females from Singapore, de Man and Tesch1 have separated this species from M. maculatus H.M.-E. on the different ratios of the anterior breadth to the length of the carapace. The figure quoted by Tesch for latifrons is 100: 84-91 and for maculatus 100 : 77-80. i- Tesch, "Siboga"-Exped., xxxixc (1918), p. 81. [ 48 ] BULL. RAFFLES CRABS OF THE FAMILY GRAPSID^S The present series of specimens have been measured with a view to obtaining this ratio, and the results are as follows:— Breadth Length Ratio Sex 29.5 mm.